The organic light emitting device is an electronic device having an anode, a cathode and an organic compound layer arranged between both these electrodes. When an exciton generated by the recombination of a hole and an electron injected from the electrodes respectively, which occurs in the organic compound layer, particularly in a light emitting layer, returns to a ground state, the organic light emitting device emits light.
The recent organic light emitting device has remarkably advanced, and is characterized in that this organic light emitting device allows a thin and lightweight organic light emitting device which has low driving voltage, various emission wavelengths and rapid response to be produced.
By the way, the organic light emitting device is roughly classified into a fluorescent light emitting device and a phosphorescent light emitting device according to the type of the exciton associated with light emission. In the phosphorescent light emitting device out of the devices, a triplet exciton participates in light emission, and the phosphorescent light emitting device is an electronic device having a phosphorescent light emitting material in an organic compound layer constituting the organic light emitting device, specifically, in the light emitting layer. Here, the phosphorescent light emitting material is excited to a triplet state by the recombination of the positive hole and the electron, and emits phosphorescence when returning to the ground state. For this reason, the phosphorescent light emitting device is an organic light emitting device which emits light originating from this triplet exciton.
By the way, the internal quantum yield of the phosphorescent light emitting device is theoretically four times the internal quantum yield of the fluorescent light emitting device, and accordingly the phosphorescent light emitting device has received attention in resent years. However, there is still room for improvement in the light emission efficiency of the phosphorescent light emitting device.
On the other hand, various materials to be used for the phosphorescent light emitting device have been proposed. For example, a compound H01 represented by the following formula is proposed as a host of the phosphorescent light emitting layer (see Patent document 1).
